Lattice Gauge Theory and (Quasi)-Conformal Technicolor

TL;DR

This study investigates whether QCD with sextet quarks exhibits walking behavior or an infrared fixed point by simulating lattice QCD at finite temperatures and analyzing phase transitions, which could indicate near-conformal dynamics.

Contribution

First lattice simulation of 2-flavor sextet quarks examining finite temperature phase transitions to distinguish between walking and conformal behavior.

Findings

Transitions are well-separated, indicating distinct confinement and chiral-symmetry breaking scales.

Coupling changes at transitions suggest finite temperature effects consistent with walking behavior.

Presence of a 3-state Wilson Line signal in the deconfined phase.

Abstract

QCD with 2 flavours of massless colour-sextet quarks is studied as a theory which might exhibit a range of scales over which the running coupling constant evolves very slowly (walks). We simulate lattice QCD with 2 flavours of sextet staggered quarks to determine whether walks, or if it has an infrared fixed point, making it a conformal field theory. Our initial simulations are performed at finite temperatures $T=1/N_ta$ ($N_t=4$ and $N_t=6$), which allows us to identify the scales of confinement and chiral-symmetry breaking from the deconfinement and chiral-symmetry restoring transitions. Unlike QCD with fundamental quarks, these two transitions appear to be well-separated. The change in coupling constants at these transitions between the two different temporal extents $N_t$, is consistent with these being finite temperature transitions for an asymptotically free theory, which favours walking behaviour. In the deconfined phase, the Wilson Line shows a 3-state signal. Between the confinement and chiral transitions, there is an additional transition where the states with Wilson Lines oriented in the directions of the complex cube roots of unity disorder into a state with a negative Wilson Line.